The present invention relates to a communication system suitable for the transmission of messages from a large number of secondary units to a primary unit, and in a presently preferred implementation relates to improvements in radio data communication systems wherein a number of mobile transceiver units are to transmit data to a base station under a wide range of operating conditions. The invention is preferably to be applicable as an upgrade of an existing data capture system wherein a number of hand-held transceiver units of an earlier design are already in the field representing a substantial economic investment in comparison to the cost of a base station.
In communication systems, various approaches have been taken to allocating use of a communications link among a large number of terminals. In a sequential polling technique, each of the terminals may be polled in sequence. Each terminal may be required to wait its turn when it has a message to send, and many terminals may be polled which have no messages to send. In a time slot type system, a general poll is sent, and terminals with messages to send respond in random ones of a series of time slots following the general poll. It is conceived that a more efficient and adaptable communication system would result from a fusion of these seemingly incompatible polling techniques.